1. Field of the Invention
The present invention relates to an apparatus and method of use thereof for drying materials, such as veneer, including a chamber at sub-atmospheric pressure with an internal heating source.
2. Description of Related Art
Traditional prior art veneer dryers use heat from a variety of sources to dry pieces of veneer or other panel materials moving through the dryers on conveyors at high temperatures and high velocities. For example, U.S. Pat. No. 3,474,544 to Holden Jr., et al. discloses a method and apparatus for changing the moisture content of veneer. By way of a conveyor system, veneer is fed at velocities of 30 to 50 mph through multiple treatment areas of the apparatus for heat treatment by high-frequency infrared, microwave or dielectric energy at temperatures between 350° F.-2300° F. Holden Jr. et al. sought to address the effect of warping as veneer was drying under older drying methods. However, in accord with the prior art dryer, the veneer was prone to scorching when heated above 270° F. by infrared energy, and the veneer was subject to checking, i.e., cracking in fissures of dry wood, as a result of rapid removal of water from the veneer.
In an attempt to address scorching and checking, other veneer dryers were designed for continuous feeding of veneer panels through a vacuum chamber on a moving conveyor in batches, but not in single sheets. For example, U.S. Pat. No. 4,146,973 to Steffensen et al. teaches a method of continuously feeding veneer into a chamber for heating under vacuum. By way of a veneer feed mechanism, pieces of veneer are separated and heated to 160° F. as they are being continuously fed through a chamber under vacuum at 250° F.-300° F. At lower temperatures and sub-atmospheric pressures, the dryer provides the means for quick and effective drying of veneer. However, the motion created by conveyors moving the veneer through the chamber tends to damage the veneer.
More modern prior art veneer dryers dry veneer panels by continuously conveying panels through a gas sealed drying chamber with pinch roll conveyors and exposing the panels to hot gases. For example, U.S. Pat. No. 4,439,930 to McMahon, Jr. teaches a modern form of conveyor dryer and method of operation. In addition, U.S. Pat. No. 4,215,489 to McMahon, Jr. teaches a roller dryer that incorporates pinch roller conveyors and heating with hot gas at sub-atmospheric gas pressure. In accord with the more modern dryers, the veneer is still damaged through the use of roller conveyors that squeeze the piece of veneer, which is also subject to damage by conveyor motion.
Accordingly, there is a present need for a single piece of veneer drying method and apparatus for quickly drying veneer by placing the piece of veneer in a dryer and by exposing the piece of veneer to suitable heat under vacuum, which avoids scorching, checking and mechanical damage to the veneer.